During an integrated circuit production process, integrated circuit chips on a semiconductor wafer are tested for their electrical parameters and functionality. For use in a circuit or electronic product, integrated circuit chips must be separated from the wafer into individual chips and are incorporated into an individual protective package. Then, they may be mounted on a surface of a ceramic substrate with other components in hybrid or multichip modules, or connected directly on a printed circuit board. The present invention is directed to a new packaging technology used to protect integrated circuit chips.
There are a large number of package types for IC chips used in the industry. One type of IC package is so structured that leads are inserted in through-holes provided on a printed circuit board. FIG. 1 shows such an example of the conventional types of IC package called a dual-in-line package. The package includes a lower part 12 and an upper part (enclosure) 11. On the lower part 12, a die-attachment area 13 is provided so that an IC chip 10 is securely attached thereto. The IC package of FIG. 1 is further provided with outer leads 14 to be connected to a printed circuit board 19, inner leads 15 continuous to the outer leads 14, bonding wires (package connection) 16 connecting die pads (electrodes) on the IC chip 10 to the inner leads 15. The IC package is covered by the enclosure (upper part) 11 for protection and heat dissipation.
The example of FIG. 1 establishes connection from the IC chip 10 to a printed circuit board 19 by the outer leads 14 which are inserted in through-holes 17 of the circuit board 19 and electrically connected therebetween by soldering. The through-holes 17 are connected to circuit patterns 18 provided on the printed circuit board 19 for electronic signal passage. The dual-in line package of FIG. 1 has a feature of thick, sturdy body with two rows of outer leads coming out of the side, resulting in a sufficient physical strength and easy handling.
However, this type of IC package has relatively long electrical paths from the IC chip to the printed circuit board, resulting in a poor high frequency performance. Moreover, the outer leads are aligned in two rows at the side of the package, which limits the maximum available number of pins (leads). Thus, the dual-in-line package is not suitable for recent, high speed, high pin count IC chips.
Another type of IC package is a surface mount package in which leads of the IC package are connected to contact pads provided on the surface of the printed circuit board. An example of surface mount package is shown in a cross sectional view of FIG. 2. The example of FIG. 2 is called a ball grid array (BGA) package which is one of the promising types of surface mount package.
In FIG. 2, an IC chip 20 is attached to a package substrate 28 through a die attach 21 such as an adhesive. Die pads on the IC chip 20 are connected to corresponding trace pads 27 on the package substrate 28 via bonding wires 22. The trace pads 27 on the upper surface of the substrate 28 are connected to trace pads 27 on the bottom surface of the substrate via through-holes 24. Each of the trace pads 27 on the bottom surface is provided with solder bump 25, which is a ball like solder. Solder masks 26 are provided between the solder bumps 25 to electrically isolate the adjacent solder bumps from one another. Under the high temperature atmosphere, the solder bumps 25 are melted to establish electric connection with contact pads on the printed circuit board.
The BGA package shown in FIG. 2 has an advantage that it has a shorter lead length, resulting in an excellent high frequency performance such as a shorter delay time and sharp rising and falling edges of pulse signals. Another advantage of the BGA is a higher pin count in a relatively small package size, allowing it to arrange a large number of pins (leads) at the bottom of the package to connect to the printed circuit board. One of the disadvantages of the BGA package, however, is that the solder connections cannot be visually inspected. Another disadvantage of the BGA is that the package is not removable or not easily removable from the printed circuit board to replace with another.